update custombootimg.mk

$(INSTALLED_BOOTIMAGE_TARGET): from build/core/Makefile
$(INSTALLED_RECOVERYIMAGE_TARGET): the same + lzma compression

Change-Id: I80bf05e2e8db99d2c1bd3fba75a01cf8bd271e2e
add BOARD_CUSTOM_BOOTIMG

Change-Id: I497d0edc209acfb25dc58818f0b70afac9520363